Now, on his last visit from Wales, my friend David dropped in a Sony 9-90UB in a bag. It's a dual-standard (405/625) 9" black and white set, made from about 1969 to 1972. It's fully transistorised, and can run off a 12V battery if required. There's a continental version, the 9-90UM, which is UHF/VHF and has 625 and 819 lines for France and Belgium. Quite why Sony developed a 405 version so late into the game seems strange, but I suppose VHF reception was better for a portable set (?) There's also a dodge for getting 625 reception on this set on VHF, and that's to gently press the 405 button so the 625 button pops out, but leaving the 405 button un-latched. I watched some Spanish TV in the early 90's via sporadic-e reception on just it's telescopic aerial!
anyway ...
"It's in bits, I had a go at fixing it...."
Fixing it? A Sony 9-90? Surely not. These sets are the most reliable in existence. I've seen dozens over the years, and, well, they just work..... Normally, if you get a vintage TV in, the last thing you do is connect it to the mains, well, with these that's exactly what you do, and they just work. Scratchy pots are the norm, but other than that, they're perfect...
... not this one.
A bit of an ominous warning on the mains plug ...
A selection of screws, knobs and trim parts....
Anyway... I'll take some shots of it, because I've never had the need to take one apart before!!
This is the power supply, It's mounted in the back. Don't undo the two screws holding the mains transformer to the back, take the back off with it in situ.
Compact chassis... wiring everywhere. Typical high quality Sony late 60's construction.
PCB....
Anyway, having checked there's nothing disconnected, and nothing looking too bad, I throw caution to the wind, remove David's "DO NOT PLUG IN" label, and plug it in, via an isolated variac.
Giving it 240 of Her Majesty's finest English volts , and nothing .... the set isn't drawing any current, so I check the fuses and mains switch, and all prove their innocence. I check mains is getting to the transformer (it is), and then check the output. Nothing. The transformer is open circuit. I then notice some wax has been melting from the transformer. It's been hot. A check on the bridge rectifier shows this to be short circuit.
To prove the rest of the set, I disconnect the output from the rectifier and connect the bench power supply....
... and at 12V, the set springs into life, and gives some results on 405 ....
.... and 625 lines. The set is drawing about 900mA from the bench supply. I look around the workshop for a suitable transformer, but I've got nothing that will supply enough current and fit in the hole....
Then I remember I bought a small switched mode supply, capable of 2A... just the job. Now these are available on eBay, but be careful when buying, as some lack the most basic of mains filtration, and are really not fit for purpose. I got a box of these from a reputable supplier. They produce almost no RFI. I connect it up to the set to prove it out...
... and once I'm happy, I mount it in place of the original transformer.
A quick check again... 405...
625....
The guilty parties....
All buttoned back up and given a soak-test for a couple of hours. It's missing the VHF channel select knob, which David seems to think is "in the living room somewhere"
And here, just to embarrass my brother Rob, is him sat in front of one back in the 80's...
... nice curtains ...
... and here's Nik-Nak's "Colour" 9-90's from the 1974 James Bond film "The Man with the Golden Gun" (c) MGM
Remember the video rack I built a while ago? It's details are here.
Well, it's developed a fault. The UHF modulator has been giving very poor pictures after a few minutes of operation. I decided to take it out, and repair it.
IF YOU HAVE ONE OF THESE UNITS, I WOULD HAVE SERIOUS RESERVATIONS ABOUT IT'S ELECTRICAL SAFETY.
I purchased it ages ago from eBay, and it came fitted with an unfused euro plug, which I cut off, and fitted a standard UK Plug, and fused it at 1 amp. I'm glad I did... read on ...
It's a useful thing. Is stable (when working properly), is adjustable throughout European VHF allocations, as well as UHF, and has switchable FM sound between 5.5 MHz and 6 MHz sound sub-carriers....
Disassembling the unit reveals a few horrors....
Check the mains input to the diminutive switched-mode supply ..... No fuse is evident!
What you can't see by this picture is the bottom of the case, the black bit. It's metal. There's no earth, which would be fine if the thing met Double Insulated (Class II) standards, which I doubt it does. You can read about classes here.
There's also zero filtering on the mains input, so any noise from the switched mode makes it's merry way back down the mains lead and out onto our mains, spoiling our radio reception (and, ironically, our TV reception too!) if it radiates (which it will).
Grim. Glad I fitted a fused plug ....
Examination of the power supply shows it to be nothing more than a simple blocking oscillator.
There's a simple zener on the output attempting to provide a little regulation. You can see where the board is a little discoloured, as it's been running warm. There are two capacitors in the primary, the mains smoothing capacitor (4.7uF 400V) proved to be very low in capacity. I fitted a 10uF , as I had one to hand. I also changed the smaller cap (10uF 50v) whilst I was there.
A quick check shows the unit to be working again.... but what to do about the safety issues?
Mounting it back in the rack, I've fitted an in line filter and fuse (100mA). I'm not so concerned about earthing the case, as the modulator is inaccessible when the rack is assembled, that doesn't mean you should be though!
Pity really ... "for a ha'p'orth of tar" an otherwise good unit is spoiled.... and possibly electrically unsafe and a fire risk. It carries a CE mark, which I've no doubt it doesn't deserve.
This gives you some idea of the size of that supply transformer, that's a 1p piece!
It's nearly my birthday, so I thought the wife may turn a blind eye to a "new" TV. There's a sort of "gap" in the collection with regards to 60's dual-standard (405 line/ 625 line) monochrome sets. Then this turned up....
It's a Ferguson 3629 "Personal" Television, using the Thorn 900 Chassis.
It's a compact set. The 900 chassis is often referred to as the "cool" chassis, designed to use less energy. It features no wasteful "dropper" resistor to obtain the correct voltages, but a mains auto transformer.
This particular set dates from 1965, and has the early valve UHF Tuner. Later models had a much improved transistor UHF tuner. The VHF Turret tuner can be seen on the right, the UHF tuner on the left. The UHF tuner has the valves enclosed in small screw-on caps.
Diminutive Mazda CME 1101 CRT
Red EHT rectifier tray. This is semi-conductor, and is mounted on top of the very reliable "jelly-pot" line output transformer.
The system switch can be seen running the whole length of the chassis. This is moved by a switch on the front panel, which moves a flexible cable, which in turn operates the system switch, and a switch on the VHF tuner.
Initial results are encouraging. Very poor frame linearity, and hold. Usually caused by a poor PCL805 or it's cathode decoupling. Not in this case, however! As usual, it was down to a capacitor on the secondary of the frame output transformer. Bob the bodger had previously been at work around the frame stage, and had fitted two replacement resistors (of the wrong value!) and a cap (of the wrong value!) After these were replaced, results on 405 lines were encouraging.
Initial results... poor linearity and frame lock.
UHF 625 operation was not good. Signals are available from my test rack at UHF channel 40, 50 and 60. In addition to signals on 36 and 68 from the house distribution system.
Reception on Ch 36 was OK, if a little grainy. Channel 60 was available strongly, although was extremely touchy to tune, and Channel 68 was good. Where are 40 and 50?
UHF tuner removed...
Valves inspected...
Fine tuning mech cleaned and lubricated. Be very careful not to move any wiring!
Apparently the small disc ceramic capacitor can crack, it's just to the left of the red coil... it's OK in this tuner.
It turns out that the PC88 is the guilty party!
Good pictures on 405....
... and 625. After a few minutes some hum starts to disturb the sound and picture.... It's pretty obvious a re-cap of the set will be required...
Quite a few caps are in physically poor condition, or electrically faulty and are replaced, along with the PC88....
The set then functions well, so I re-install the chassis into the cabinet. The set then suffers with intermittent frame collapse (no frame drive), leaving a horizontal line on the centre of the CRT....
After much probing about with an insulated screwdriver, I spot something arcing on the scan coils...
... it's a thermistor (or rather was!). It's turned into a blob of something... I don't have a replacement (and I've got precious little chance of getting one), so I shorted it out, restoring operation.
Ugh ... soundbars. No. Not for me. A decent amp and speakers, why not? But the thought of an amp and speakers placed in a tiny enclosure to put under your telly, to improve the (usually) woefully inadequate speakers in a flat screen ... anyway ... rant over.
This is the Panasonic SC-HTB10 sound bar. It belongs to a colleague.
"It just clicks. Can you have a look?"
Yeah , why not...
Dis-assembly involves removal of the myriad of screws from the back, there are 4 hidden under rubber bungs on the corners. The back fits really tightly, I needed to gently pry it free using a "spudger" (one of those cheap plastic tools you get for taking mobile phones apart).
This is the only time I've ever had to take a photo of a piece of kit in panorama mode!
You'll need to disconnect the sub-woofer which is in the back...
Neat tuning port!
Unplug the other two speaker plugs (blue and white, just by the green circuit board)
You should now be able to lift the electronics clear from the case.
Now, I'll just draw your attention to the disclaimer up there on the right of the webpage. Yep, that one. I'm doing that, because this one caught me out a bit. Under the pressed steel shield is the power supply (actually two supplies). Because of the symptoms, my guess was it was failing to start up. I carefully removed the shield and removed the supply.
Now, we can see there are two switched mode supplies. There's a small switched mode transformer above the date code, and a larger one below.
The small power supply supplies the micro-processor and control electronics. It's always on, so the remote is kept powered. This appeared to be functioning correctly.
The larger power supply, and the components in the area marked "HOT" are used to supply the amplifiers, This is where the fault lay. Despite the fact that this supply had been disconnected for many minutes, the large electrolytic still held an impressive ~300V DC. Whilst I avoided getting a shock, I was surprised to find this charge still remained. Having safely discharged the cap with a watty 10K resistor, I started a few checks. See how dis-coloured the board is around the switched mode controller and chopper IC 5701? Thing's have been running HOT! (The HOT marking on the board is to warn you that this part of the power supply is connected to live mains, and is not isolated! Not the temperature of the electronics!) Poor old C5726 had suffered as a result. It's ESR had risen to about 25 ohms... far too much for this capacitor to be in any health. A replacement was fitted and restored operation!
Now, a few years back, I restored a 1951 Bush TV22 for my friend Colin.
I made a video at the time...
The Bush TV22 is a very common set, even now. They seem to crop up at regular intervals on eBay. It's a 9" TRF set, and had various modifications and different designs during it's long production run.
Now this set was used regularly until last year, when Colin rang to say it was acting up a bit, and could I take a look... sure.
And so it arrived. Poor line linearity and decreasing width as the set warmed up, over a period of 30 mins or so. Not good symptoms for a vintage television, as it's usually signs that the line output transformer is on it's way out, and good secondhand transformers are difficult to find, and new ones unobtainable.
That proved to be the cause with this set. Thankfully the Bush transformer is quite simple, and there's a marvelous chap called Ed, who can rewind the things. It's unusual to find a duff high voltage EHT winding in the Bush set, which is a blessing, as rewinding this part is not possible, So it's the primary and lower voltage secondaries that fail. Off to Ed it goes....
... Within a few days it returns, nicely rewound, and I reinstall it into the set .... the line stage warms up, and whistles strongly (a good sign). There's no glow from the EHT rectifier valve, and no EHT. I check the line stage from one end to the other. Nothing amiss... ???
I remove the transformer again, and perform a "ring" test. This is a basic test to ensure the transformer has no shorted turns. If it was the overwind, there's a few options open to me to create some EHT to drive the final anode of the CRT without using the overwind.
The ring test involves connecting the transformer to the square wave calibrator on your oscilloscope, at the end which is usually fed from the anode of the line output valve, and connecting the scope probe to the eht wiinding.
The ring test allows the transformer to oscillate. The more oscillations, the better the transformer.
That all looks great...
A duff transformer looks like this.. See the "ringing" stops well before the next cycle...
A few emails swap between myself and Ed. It appears the transformer for this set was very unusual in it's construction, and one Ed had seen before. Some of the windings appeared to have been wound "out of phase" with usual convention. Could this be the cause of the issue? I experimented by removing the EHT overwind, and slotting it back onto the transformer upside down. It worked after a fashion, but the EHT was still very low. Ed asked me to return the transformer to him for further investigation.
A few days elapsed, and the second rewind arrived back. Whilst the transformer was now functioning, the EHT was still low at around 4KV (it should be ~7.5KV), and there was terrible line fold-over which I couldn't get rid of...
To take the above picture, I needed more than the available 4KV, so I had previously purchased this little device from eBay...
Described as a DC 3V to 7KV 7000V Boost Step-up Power Module High-voltage Converter Generator, a useful addition to the armory of test gear. I wouldn't recommend shorting it out like the picture! Anyway, this provided some EHT to show the picture above.
Then lady luck smiled on me... and this set arrived as a gift. Apparently found on a tip! There's a small crack to the bakelite case, but it's almost invisible. I don't actually own one of these sets, so it was most welcome.
Naked, and filthy!
Line output stage cover removed ... and dusty!
First things first, and hook up the Leader CRT-910A tube analyser to see if it's worth pursuing. If the CRT is bad, it won't be worth doing anything with.
The needle slowly swings into action ... and rises.... and rises ... 95%! I find this hard to believe, perhaps the analyser has developed a fault.... but checks on another tube show it's telling the truth!
So, I hatch a plan. Do a quick restore on the gifted set, in an attempt to prove the line output transformer. If it's OK, swap the transformer over to prove that the rewound transformer still has issues, or not, as the case may be ....
Now this model was later, and has a different receiver (or RF deck) than the one we are repairing, which is a pity, as I was just hoping to fix the top chassis, which contains the power supply, line and frame stages, and just swap out the working receiver from Colin's set... not to be.
So, our tube (CRT) is good, so first, remove the mains smoothing capacitor, and give it a few hours on the ole' Dreadnaught capacitor reformer...
It takes a while, but comes up well...
Next up is to re-cap the frame stage. This is located on tag-strip on one side of the chassis. It's essential to do this before applying power, to avoid damaging the frame blocking oscillator transformer (Ed rewinds these too!)
Then to re-cap the underside of the main chassis. Anything with wax insulation will be faulty (if not now, within hours of first use) and electrically leaky, so they are evicted on sight. There are two located under the tag-strip, which needs careful removal.
Whilst I'm doing this, I notice the line output transformer is different in appearance to the original in Colin's set. Thankfully this is simply a later revision, and the two are electrically identical.
A nicely dated capacitor shows the set was made late 1952.
Tag-strip with line output components re-capped. (There's one on the sound transformer to change yet! Can you spot it?)
Then onto the receiver or RF deck...
Half-way there!
And, once finished, on with some mains!
EHT rises, and eventually settles on ~8KV
And, after some alignment issues with the front end of the RF Deck... pictures :)
Pictures were taken in a mirror...
The set isn't finished by a long-way, as there's much rubber insulated wiring that has degraded and become brittle, but it's proved a point.
So the known good transformer is removed from the set, and an adaptor bracket is made, so we can mount it into Colin's set, as the two transformers are cosmetically different.
And Colin's set produces a good picture!
I check the resistances on all the windings, and between the windings on both transformers. They are identical... I measure the inductances on all the windings, both transformers measure the same. I have another word with Ed, and he asks me to send him both the known good transformer and the re-wound one. Ed finds the only difference between the transformers is the inter-winding capacitance. After a few test windings, Ed succeeds in making two transformers that measure identically.... and, sure enough I fit the freshly re-wound transformer back into Colin's set, and, with bated breath, switch on!
Results!
Back in it's cabinet, and undergoing a soak test for a few hours!
Big thanks to Ed for his incredible diagnostic and re-winding skills, and thanks to Colin, for donating this lovely 20" Sony Widescreen..
Apparently there's a 16" too ... that would be nice ;)
A bit of an ominous warning on the mains plug ...
Giving it 240 of Her Majesty's finest English volts , and nothing .... the set isn't drawing any current, so I check the fuses and mains switch, and all prove their innocence. I check mains is getting to the transformer (it is), and then check the output. Nothing. The transformer is open circuit. I then notice some wax has been melting from the transformer. It's been hot. A check on the bridge rectifier shows this to be short circuit.
